Plasma treated tubing

ABSTRACT

Polymeric tubing having an outer surface with a reduced coefficient of friction. The outer surface is treated by an exposure to a plasma glow discharge in the presence of an inert gas, and by deposition of a monomer during exposure to the plasma glow discharge for a time sufficient to modify the slip characteristics of the surface of the tube. The tube is preferably exposed to plasma glow discharge for a time sufficient to reduce the coefficient of friction by at least 70%. The tubing may be fabricated of silicone rubber, and the monomer deposited may be N-vinyl-2-pyrrolidone.

This application is a divisional application of U.S. patent appln. Ser.No. 08/923,046 filed Sep. 3, 1997 entitled "Plasma Process for ReducingFriction on Polymeric Surfaces" to Stewart et al.

BACKGROUND OF THE INVENTION

This invention relates to surface modification of the slipcharacteristics of polymeric surfaces. In particular, surfaces of tubingcomposed of polymeric materials such a silicone rubber, polypropylene,polyethylene, polyvinylchloride, fluoropolymers and the like or otherdielectric materials and to improved methods and apparatuses foreffecting such modifications.

Polymeric plastic tubing, particularly that of small diameter, and mostespecially that of silicone rubber, is used in many medical applicationsand devices. In particular, silicone rubber (especially cross linkedsilicone elastomer with silica filling) is the polymer of choice fortubing in many medical applications involving implantation.

Catheters prepared from polymeric materials are used frequently in suchroutine procedures as the delivery of intravenous fluids, removal ofurine from compromised patients, chemical sensing using a variety ofchemical transducers, monitoring cardiovascular dynamics, and treatingcardiac and vascular disorders. Catheters provide the pathway topreviously inaccessible body areas for both diagnostic and therapeuticprocedures, thereby reducing the need for surgery. For example, doublecatheter systems are utilized for drug delivery or occlusion of bloodflow to specific organs or tissues. Typically, a rigid outer catheterand a buoyant, flexible inner catheter that can freely float in theblood stream are used in such procedures. Another example is a pacinglead which utilizes a small diameter tubing such as less than 0.055 inch(1.40 mm) (OD) with an inner diameter (ID) of 0.35 inch (0.9 mm). Inthis type of lead, an elongate wire core (usually in the form of a coil)having a helical screw-in electrode at its distal end is placed insidethe small diameter tubing to provide a catheter-like device. The corewire is manipulated at the proximal end of this arrangement by thephysician during implantation to screw the helical electrode into hearttissue and fix the lead in place. Of course these catheter-like devicesmay involve other structures not described herein for simplicity.

As catheterization techniques have become more complicated, more demandsplaced on the performance of the catheter have increased. For instance,the paths that these catheters must take through the body are often longand tortuous, such as accessing the cranial vessels via the femoralartery. The polymeric materials from which catheters are made, such assilicone rubber, have a tacky surface upon exposure to an aqueousenvironment. This causes excessive friction, making placement of thecatheter-like device in the body difficult. Further, these frictioncharacteristics also make torque transfer through the tubing difficultthus, for example, making difficult the turning of the core wire whichis preferably a torsion coil in the aforementioned "screw in" pacinglead to screw the helical electrode into tissue.

Previous practices to ameliorate these friction characteristics haveinvolved: 1) the use of harder materials which are more slippery butless biostable and less suitable for implantation, e.g., polyurethane;2) coating; 3) hardening; 4) swelling; and even 5) the use ofenvironmentally unfriendly materials such as chlorofluorocarbons (CFC).For example, polyurethane catheters have been coated with a compositionof a poly(vinyl pyrrolidone) (PVP) crosslinked with an isocyanate(commercially available under the trade designation "HYDROMER" fromHydromer Inc., New Jersey). See, e.g., "Reduced Frictional Resistance ofPolyurethane Catheter by Means of a Surface Coating Procedure," byNurdin, N., et al., Journal of Applied Polymer Science, Vol. 61,1939-1948 (1996), herein incorporated by reference.

Plasma discharge has also been used on tubing with some degree ofsuccess. More specifically, exposure of polymeric surfaces to plasmadischarge is effective in modifying the surface to improve its slipcharacteristics. For example, U.S. Pat. No. 5,593,550 (Stewart et al.)is directed to a plasma process for improving the slip characteristicsof polymeric tubing on its OD and ID. U.S. Pat. No. 5,133,422 (Coury etal.) is directed to improving the slip characteristics of polymerictubing on its OD by plasma treatment in the presence of a gas selectedfrom the group consisting of hydrogen, nitrogen, ammonia, oxygen, carbondioxide, C₂ F₆, C₂ F₄, C₃ F₆, C₂ H₄ C₂ H₂, CH₄, and mixtures thereof.U.S. Pat. No. 4,692,347 (Yasuda) is directed to plasma deposition ofcoatings and to improving blood compatibility on both the OD and the IDsurfaces of polymeric tubing by coating it under discharge conditions ina single chamber.

The theory and practice of radio frequency (RF) gas discharge isexplained in detail in 1) "Gas-Discharge Techniques For BiomaterialModifications" by Gombatz and Hoffman, CRC Critical Reviews inBiocompatibility, Vol. 4, Issue 1 (1987) pp 1-42; 2) "SurfaceModification and Evaluation of Some Commonly Used Catheter Materials ISurface Properties" by Triolo and Andrade, Journal of BiomedicalMaterials Research, Vol. 17, 129-147 (1983), and 3) "SurfaceModification and Evaluation of Some Commonly Used Catheter Materials,II. Friction Characterized" also by Triolo and Andrade, Journal ofBiomedical Materials Research, Vol. 17, 149-165 (1983). All of theforegoing are incorporated herein by reference.

A number of patents have been reviewed in which plasma reactors aredisclosed which use wave energy (RF or microwave) to excite plasma.Although not admitted as prior art, examples of plasma reactors andmethods using the same can be found in the issued U.S. patents listed inTable 1 below.

    ______________________________________                                        LIST OF U.S. PATENTS                                                          ______________________________________                                        U.S. Pat. No. 5,593,550                                                                       01/14/1997 Stewart et al.                                     U.S. Pat. No. 5,244,654                                                                       09/14/1993 Narayanan                                          U.S. Pat. No. 5,223,308                                                                       06/29/1993 Doehler                                            U.S. Pat. No. 5,133,986                                                                       07/28/1992 Blum et al.                                        U.S. Pat. No. 5,133,422                                                                       07/28/1992 Coury et al.                                       U.S. Pat. No. 4,948,628                                                                       08/14/1990 Montgomery et al.                                  U.S. Pat. No. 4,927,676                                                                       05/22/1990 Williams et al.                                    U.S. Pat. No. 4,846,101                                                                       07/11/1989 Montgomery et al.                                  U.S. Pat. No. 4,752,426                                                                       06/21/1988 Cho                                                U.S. Pat. No. 4,718,907                                                                       01/12/1988 Karwoski et al.                                    U.S. Pat. No. 4,692,347                                                                       09/08/1987 Yasuda                                             U.S. Pat. No. 4,448,954                                                                       12/18/1984 Hatada et al.                                      U.S. Pat. No. 4,261,806                                                                       04/14/1981 Asai et al.                                        ______________________________________                                    

It is a primary object of this invention to provide polymeric surfaceswhich exhibits improved slip characteristics. This and other objectswill be clear from the following description.

SUMMARY OF THE INVENTION

Although this invention is applicable to surfaces of polymeric materialsand dielectric materials, it will be described herein with particularreference to silicone rubber tubing, one preferred embodiment of theinvention. It has been discovered according to this invention that glowdischarge coupled with monomer deposition can make a surface ofpolymeric tubing more lubricious. Preferably, polymeric tubing is placedwithin a glass reactor or other glow discharge chamber (preferably thickwalled glass or a suitable ceramic) which receives the tubinglongitudinally. The glow discharge electrodes are applied to the glassreactor or discharge chamber with the plasma discharge gas being insidethe glass reactor. The tubing is next passed within a second glassreactor similar to that described above except that a monomer isdischarged in the glass reactor. Generally, any electricallynon-conductive dielectric reactor chamber means which holds a vacuumwill suffice as a discharge chamber. It can be applied to any polymericsurface, such as tubing of any size diameter.

The absolute size of the space relationship between the OD of thepolymer tubing and the ID of the glass tube (i.e., "reactor" or"discharge chamber") or other chamber in any given instance will dependon many variables e.g., gas pressure, power applied, relative size ofspace in the glass tube and the size of the polymeric tubing, and soforth.

For example, the following treatment conditions have provided tubingwith a desirable outer surface with respect to its improved slipperycharacteristics: OD of glass tube is about 0.5" to about 1.5"; thelength of the glass tube from about 3" to about 18"; RF power between300 watts and 30 watts that can be continuous or pulsed power mode, suchas about 1 millisecond to about 10 milliseconds; and gas pressure in theplasma reactor of about 0.010 Torr to about 10.0 Torr. The use of pulsedpower is an important factor in practicing this invention so that aportion of the monomer is activated to initiate polymerization withoutsubstantially adversely affecting pendant functional groups on themonomer.

In any given instance, it can be readily determined empirically byvarying discharge conditions and time of exposure to discharge as towhat treatment results are obtained and adjusting the conditions toobtain the desired result.

For purposes of this invention, the gas discharge process or radiofrequency discharge as contemplated herein need only be such as to giverise to a plasma glow discharge which interacts with surfaces exposedthereto, such as silicone rubber, to alter same by reaction therewith.The plasma discharge apparatus will include a glow discharge chamber orreactor as aforementioned including electric reactor for connection to aradio frequency power source or the like for reactance coupling uponapplication of power from the source. Also included is a monomerdeposition chamber or monomer reactor for exposing the polymer tubing toa zone in which a monomer is deposited on the surface of the polymertubing. As in the glow discharge chamber, the monomer deposition chamberincludes electric reactor for connection to a radio frequency powersource or the like for activation of the monomer upon application ofpower and exposure to a monomer vapor from a monomer source.

The reactor apparatus of the invention and the method thereof overcomesproblems of the designs described in the patent literature as follows:

Tubing Length Limitation: The present apparatus can treat the OD surfaceof virtually unlimited lengths of tubing. The only limitation is howlarge a spool can be fitted inside of the vacuum chamber. A typicalreactor will have a capacity of 1,000 to about 5,000 feet depending ontubing diameter.

Control of Deposition Chemistry: Short pulses of high power, such asabout 10 watts to about 300 watts for about 1 to about 10 milliseconds,interrupted by longer "off" periods (about 4 to about 800 milliseconds)provide enough energy to activate the monomer yet limit its overallintensity so that pendant functional groups on the monomer are notsignificantly adversely altered during deposition. Thus, the use ofpulsed power is critical to the success of the method because activationof the monomer is desired without substantially altering the chemicaland/or physical characteristics of the monomer during deposition.Accordingly, the present invention relates to the deposition of amonomer to glow discharge pre-treated tubing.

Treatment of Both Outer and Inner Surfaces: In one embodiment, anapparatus and method of the invention utilizes three separate zones inwhich to first pre-treat the outside of the tubing, treat the insidesurface of the tubing and then deposit the monomer on the pre-treatedoutside surface of the tubing. This is important when treating verysmall tubing. The small tubing requires a very close fit inside of theID treatment zone tube to prevent a discharge between tubing and glassas is described in U.S. Pat. No. 4,448,954. This can lead to problemswith the tubing sticking inside of the glass tube reactor. However, inthe present reactor and method the OD plasma pre-treatment is preferablyperformed on the tubing prior to its entry into the ID zone fortreatment which aides in reducing the friction between the outside ofthe tubing and reactor to prevent sticking.

Tubing Manageability: Applicants have recognized that providing alubricious surface on tubing or a catheter should be balanced with theability of the physician or technician to handle the device during aprocedure. For example, it has been reported that certain surfacetreatments and/or coatings cause the tubing or catheter to become veryslimy and slippery when wet. Thus, the physician may have difficultyguiding the catheter to the desired internal location or suturing a leadbody to surrounding tissue, for example. Additionally, a portion of thecoating may desorb from the surface of the catheter on to thephysician's gloves during the procedure which, again, may adverselyaffect the physician's control of the device. The present invention isdirected to the attachment of the monomer to, preferably, the OD surfaceso that it is stable during manipulation, i.e., plasma polymerized(abbreviated herein as "pp") monomer is less likely to desorb from thetubing surface.

Polymer Surface Dynamics: One of the difficulties in modifying polymersurfaces relates to the mobile nature of amorphous polymer molecules. Ifa modification, such as oxidation, of a surface is performed, molecularmotions can, over a period of time, cause the modified surface tointermingle and diffuse into the polymer matrix. This tendency is mostpronounced in silicone elastomers which have very mobile polymer chains.To overcome this problem, plasma treatments may be used to crosslink andstabilize the polymeric surface. However, within hours or even minutesafter plasma treatment, the surface begins to revert back to itsoriginal hydrophobic state. Uncrosslinked oligomers and low molecularweight oils begin to bloom to the polymeric surface. These oils tend tointerfere with attachment or grafting of coatings to the polymersurface. A particularly preferred way to overcome this time dependentphenomenon is to inert gas plasma treat the polymeric surfaceimmediately followed by a modification step, preferably deposition of asuitable monomer, before the polymeric surface begins to revert. In sodoing, a polymeric surface can be modified to a relatively long lastinghydrophilic surface.

Other improved properties resulting from coatings and treatmentsaccording to the invention are:

reduced permeability to fluids and gases;

reduced "cold flow" of silicone surfaces;

provision of specific surface chemistries by selection of functionalcoatings; and

bondability with adhesives and molding compounds.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a showing of an apparatus according to the invention forplasma discharge pre-treating and depositing a monomer on an OD surfaceon a continuous basis;

FIG. 2 is a detailed showing of the OD pre-treatment zone of theapparatus of FIG. 1;

FIG. 3 is a detailed showing of the transition zone between the plasmapre-treatment and the monomer deposition zones of the apparatus of FIG.1; and

FIG. 4 is a detailed showing of the monomer deposition zone of theapparatus of FIG. 3;

FIG. 5 is a typical schematic arrangement showing how a piece ofpolymeric tubing is held in a reactor for plasma discharge;

FIG. 6 is a showing of an apparatus according to the invention forplasma discharge treating a coiled length of tubing preferentially onits ID;

FIG. 7 is a simplified schematic of an implantable medical device inaccordance with the invention;

FIG. 8 is a simplified schematic of an implantable medical device inaccordance with the invention as it relates to a patient's heart;

FIG. 9 is a block diagram illustrating constituent components of oneembodiment in accordance with the invention;

FIG. 10 is an overlay FTIR spectrum of silicone tubing treated inaccordance with the invention;

FIG. 11 is a graphic representation of monomer retention percents oftubing treated in accordance with the invention;

FIG. 12 is a graphic representation of repeated friction tests performedin an aqueous environment with tubing treated in accordance with theinvention; and

FIG. 13 is a graphic representation of friction tests performed in anaqueous environment with tubing treated in accordance with theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention provides a plasma reactor apparatus and method whichproduces an improved slip characteristic of polymeric surfaces such asan outer diameter (OD) surface of a polymeric tubing, such as siliconetubing. Improved slip characteristic refers to lower friction uponexposure of tubing treated in accordance with the invention to anaqueous environment when compared to untreated tubing. The treatment hasbeen demonstrated to uniformly improve, increase the lubricity of, thesurface of the tubing. It is believed that the method of the inventioncauses increased bonding of a monomer to the polymeric surface of thetubing, such as by covalent attachment.

The method of the invention is preferably performed continuously meaningthat tubing is fed from a spool of 1,000+ feet of tubing and treated, inone preferred embodiment, as it moves through an inert gas plasma glowdischarge pre-treatment zone and then a monomer deposition zone of thereactor apparatus after which it passes into a receiving chamber. Theplasma glow discharge pre-treatment and the monomer deposition zoneseach includes a set of radio frequency electrodes or a microwave cavity.In the pre-treatment zone of the apparatus, preferably located justprior to the monomer deposition zone, the outside of the silicone tubingis preferably glow discharge treated to prepare the OD surface of thetubing for monomer deposition in a subsequent zone. This outerpre-treatment zone may include a 0.5 inch or larger glass tube aroundwhich is a set of radio frequency electrodes, a coil or a microwavecavity used to excite a glow discharge around the outside of the plastictubing.

The glow discharge pre-treatment of the outside of the polymeric tubingdescribed above may involve the use of "inert" gases, i.e., gases thatwill not polymerize under plasma discharge conditions as set forthherein. Preferably, inert gases are selected from the group of helium,neon, argon, nitrogen, and combinations thereof. Combinations of theinert gases can also be beneficial to make the initiation of thedischarge easier. The polymeric tubing is filled with gas to a stablepressure while the pre-treatment zone is maintained at a relativelylower pressure which is usually more desirable for the outer surfaceplasma treatment. Pressure differentials are not critical but can bedesirable. These differential pressures are maintained by using gas flowcontrols, orifices, and automatic exhaust valve pressure controllers(not shown in any detail).

In another sense, this invention provides tubing having modified slipcharacteristics on the inside surfaces thereof particularly smalldiameter silicone tubing of less than about 1 mm in OD. This isaccomplished by means of plasma discharge within the tubing. Improvedapparatus for accomplishing this is also provided.

In FIG. 1, the pre-treatment zone 60 is the first plasma that the tubing18 passes through after coming off of reel 30. The top of this sectionof the apparatus seals against the underside of the top plate assembly40. The bottom of this section seals against the "transition zone" block62. In the pre-treatment zone 60, the tubing 18 receives an inert gasplasma pre-treatment on its outer surface.

Upon entry into pre-treatment or glow discharge zone 60, the tubing maypass through a close fitting orifice 68, best seen in FIG. 2, whichgenerally should have a diameter equal to the tubing nominal OD plus0.001 in ±0.001 in. This diameter may vary depending on the type oftubing and type of treatment or coating to be performed. For tubing0.054" OD the orifice should be drilled to about 0.055". This size maylater be adjusted to achieve precise pressure differentials. The orificeserves to a) prevent the glow discharge from spreading into the uppertubing reel chamber 38, b) allow different pressures or types of gassesto be maintained in the upper chamber 38 and pre-treatment zone 60, c)guide the tubing 18 down the center of the pre-treatment zone 60, and d)allow a small gas flow from the upper chamber 38 to the glass tube 69below where a vacuum exhaust line 71 may be arranged to carry away theflow.

The pre-treatment zone 60 typically includes a section of glass tube 69which is commonly available as a sanitary glass tube. The length of theglass tube 69 may typically be from about 3 to about 18 inches inlength, more preferably from about 6 to about 12 inches in length, andmost preferably from about 6 to about 10 inches in length. The glasstube 69 should be capable of forming a vacuum seal with each end of thetube butting up against a O-ring 70, see FIG. 2. Provision is made toallow for entry of gases below the orifice 68 and above the end of theglass tube 69.

Preferably, the glass tube 69 has a diameter sufficiently large so thatthe pre-treatment of the OD surface is substantially uniform. Morepreferably, the diameter is about 0.5" to about 1.5" and mostpreferably, about 1.5". When the OD of the glass tube 69 is less thanabout 0.5", the tubing 18 must be substantially centered in order tomaintain a uniform glow discharge at lower gas pressures. Thus, a largerglass tube 69 tolerates more misalignment and provides a more uniformdischarge around the tubing 18.

A plurality of circular disc or torus shaped electrodes, shown as 76 and78 in FIG. 2, are dimensioned to suit the diameter and length of theglass tube 69. A PTFE insulator support bar 46 may be included as shownin FIG. 2. The two ground electrodes 76 may be connected by a commonground strap 80, also shown in FIG. 2.

As the tubing 18 passes through the pre-treatment zone 60, a glowdischarge is produced by the inert gas, as defined above, by reactancecoupling utilizing power provided by the radio frequency power source,shown as electrodes 76 and 78. Under plasma discharge conditions, theinert gas treatment stabilizes the polymeric surface of the tubing inpreparation for application of the monomer. While not wishing to bebound by any particular theory, it is believed that pre-treatment byinert gas plasma causes the polymeric surface of the tubing 18 tocrosslink and form a population of free radical sites.

Transition Zone, zone 82--see FIG. 3 in particular, serves as aconnection between the pre-treatment zone 60 and the monomer depositionzone 66. Preferably, the transition zone 82 should a) be capable offorming a vacuum seal with the lower end to the pre-treatment glass tube69, b) connect with the compression fitting 50 of the monomer depositionzone 66 below it, c) provide a vacuum port 84 which connects to anautomatic throttle valve pressure controller (this allows gas flow whichenters through or below the orifice 68 at the top of the pre-treatmentzone 60 to be drawn off below the pre-treatment zone), and d) provide arigid connection to the upper end of the monomer deposition zone 66 inorder to minimize or prevent any relative motion between the top andbottom compression fittings 50 of the monomer deposition zone 66.

The Monomer Deposition Zone 66 (see FIG. 4 in particular) performs themonomer deposition on the OD surface of the tubing 18 as it movesthrough the deposition zone 66. In the monomer deposition zone 66, amonomer is delivered as a vapor to a very low energy glow dischargezone. Preferably the monomer deposition zone 66 includes an electrodeand glass tube configuration similar to that shown in FIG. 2. Thepre-treatment on the outer surface tubing 18 in the pre-treatment zone60 is preferably performed prior to entry into the glass tube 69'.

More importantly, it was found that the plasma pre-treatment of thetubing was critical to obtaining a stable wettable surface afterdeposition of the monomer. For example, it was found that when theplasma pre-treatment was not uniform around the surface of the tubing,improved slip characteristics were only observed on that portion of thetubing surface that was pretreated.

It was also found that when fully treated tubing was rinsed and soakedovernight in deionized water at room temperature, the tubing wasobserved to retain a wettable surface. This indicated that the monomerdeposition was retained and it is believed that the monomer is bound tothe tubing surface. This has been shown by means of IR spectra (FTIR)and friction analysis.

The length of the glass tube 69' is preferably about 6 inches to about12 inches if using capacitive electrodes. Also, if a helical resonatorplasma excitation (13.56 Mhz) source is used, a tube length of close to18 inches may be required.

Electrode configuration may vary. However, the circular disc or torusshaped electrodes 76' and 78' are dimensioned to suit the diameter andlength of the OD tube 69', as described with respect to thepre-treatment zone 60. Also, a PTFE insulator support bar 46 may beincluded as shown in FIG. 4. The two ground electrodes 76 may beconnected by a common ground strap 80 also as shown in FIG. 4. In otherwords, the configuration may be similar to that in the pre-treatmentzone 60, described above.

In addition to an electrode configuration and a glass tube, the monomerdeposition zone 66 further includes a monomer source 55, as shown inFIG. 4. The monomer source 55 typically includes a monomer reservoir 52,a mass flow controller 58, a monomer conduit 54 and a monomer inlet 51.

Preferably, a monomer, typically liquid or gas, is held in the monomerreservoir 52. Suitable monomers for use in the present inventionincludes a compound comprising a polymerizable structure selected fromthe group of a carbon-carbon double or triple bond, a saturated cyclicgroup, an arylene group, and mixtures thereof; and one or more pendantfunctional groups selected from the group of an amine, a hydroxyl, acarbonyl, a carboxylic, an amide, a sulfone, an ether, an ester, anepoxide, and mixtures thereof. A particularly preferred monomer isN-vinyl-2-pyrrolidone (NVP).

The monomer is discharged through the monomer conduit 54 to the monomerinlet 51, where the monomer enters the glass tube 69' of the monomerdeposition zone 66. Preferably, the monomer conduit 54 is heated to atemperature approximately equal to or greater than the boiling point ofthe monomer so that the monomer can be introduced in the monomerdeposition chamber 66 without condensation as a monomer vapor. Forexample, when the monomer is N-vinyl-2-pyrrolidone, the monomer conduit54 is at a temperature of about 80° C. or greater.

The monomer source 55 may optionally include a by-pass valve 56 aroundthe monomer mass flow controller 58 for removal of monomer reservoirheadspace gases prior to the flow of the monomer vapor through themonomer mass flow controller.

Accordingly, for example, it is desirable to provide a flow of NVP vaporto a low energy glow discharge, e.g., about 0.1 to about 100 sccm. Whilenot wishing to be bound by any particular theory, it is believed that byproviding low radio frequency power to the monomer deposition zone 66,the discharge primarily activates only the vinyl groups on the NVPmonomer, i.e., mildly activating and initiating polymerization of themonomer. Further, it is believed that the mild activation of the monomerin combination with the free radical sites on the polymeric surface ofthe tubing 18 produced in the pre-treatment zone 60 allows thepolymerization of the monomer to proceed without significant alterationof the monomer structure. It is believed that conventional plasmadepositions utilize greater energy in the deposition plasma in order tosufficiently activate and stabilize the polymeric surface, i.e., so thatthe monomer would adhere to the polymeric surface. It is furtherbelieved that conventional plasma depositions cause the monomer toretain few chemical and physical properties due to molecularfragmentation that occurs at high energy plasma.

Reference to FIG. 5 schematically shows a preferred configuration of theelectrodes and glass tubing for plasma discharge according to oneembodiment of the invention. In general, the configuration is useful inthe pre-treatment zone 60 and the monomer deposition zone 66 (exceptwhere noted). A plasma discharge apparatus generally indicated at 10 isenclosed within an evacuated environment 12. In the pre-treatment zone60, the evacuated environment 12 may contain an inert gas, preferably aninert gas selected from the group of nitrogen, helium, neon, argon, andmixtures thereof. More preferably, the gas is argon. The gas is at asuitable pressure for discharge such as 0.6 torr. In the monomerdeposition zone 66, the evacuated environment 12 may contain themonomer. It was found that the coefficient of sliding friction betweenthe outer diameter surface of a silicone tube and metal can be reducedby about 70% or more with the treatment of the present invention.

The discharge apparatus 10 of FIG. 1 includes a glass reactor and holdertube 69 having a bore 16 therethrough, that is useful in both thepre-treatment zone 60 and the monomer deposition zone 66. Also useful inboth zones is a plurality of circular, torus shaped ground electrodes76, preferably two, and an RF powered electrode 78 that encircle glasstube 69, as shown.

In the pre-treatment zone 60, the RF powered electrode 78 is preferablyoperated in a continuous mode. For example, it has been found that apower level of about 20 watts to about 300 watts at a continuous modewas effective to pre-treat the tubing so as to permit a substantiallyuniform deposition of the monomer. In the monomer deposition zone 66,the RF power electrode 78' is preferably operated in a pulse mode. Forexample, it has been found that pulsing between about 100 watts andabout 0 watts for about 2 milliseconds to about 20 milliseconds producedan effective monomer discharge. More preferably, the pulsed power sourceprovides a continuous sequence of "on" periods and "off" periods, wherethe "on" periods having a duration of about 1 to about 3 millisecondsand the "off" periods have a duration of about 4 to about 20milliseconds.

In an arrangement such as that shown in FIG. 5, if the length of thetubing 18 is greater than the length of the discharge zone between theelectrodes 76 and 78, it will be desirable to make provisions to providedischarge throughout the entire length of the tubing. This may beaccomplished in a variety of ways. For example, additional sets ofelectrodes can be distributed over the length of the apparatus. Also, anarrangement may be provided (not shown) in which the set of electrodesmove over the length of the apparatus. Most preferably, the arrangementwill be modified to allow the tubing 18 to move through the bore 16 asby being pulled therethrough thus passing the tubing through thedischarge zone which exists between the electrodes. An embodiment ofthis latter preferred arrangement, including both the pre-treatment zone60 and the monomer deposition zone 66, is shown schematically in FIG. 2.Continuous tension is preferred to avoid having the polymeric tube stickin the reactor.

The apparatus of FIG. 1 shows the tubing 18 held on a reel 30 at the top(or inlet end) of the apparatus from which it is pulled by a means suchas a tubing transport track drive generally indicated at 32 which ispositioned at the bottom (or outlet end) of the apparatus, shown indetail in FIG. 4. The track drive may include a pair of electricallydriven controlled speed drive belts 34 and 36. Other arrangements forpulling the tubing through the apparatus will be apparent to thosefamiliar with this art.

As shown in FIG. 1, the reel 30 and the supply of tubing 18 it carriesare maintained within a sealed environment by means of a bell jar or thelike 38 which seals against an upper plate 40. Likewise, the treatedtubing which is collected at the bottom of the apparatus is containedwithin a sealed environment provided by bell jar arrangement 42 whichseals against bottom plate 44, as depicted in FIG. 4. Other means forproviding sealed chamber arrangements will be readily apparent to thosefamiliar with this art.

The gas environment is provided by evacuating bell jars 38 and 42 bymeans of a vacuum pump connected to outlet arrangement (not shown).Because glass tube 69 (69') is in sealed communication with both 38 and42 the entire system is evacuated in this manner. Other chamber designsmay be used. The selected discharge gas, such as argon in this instance,is introduced to the system through inlet arrangement 41 to a pressuresuch as 0.6 Torr.

Because it is desirable to plasma discharge pre-treat the tubing 18prior to a preferred apparatus has been described that includes threezones--a pre-treatment zone 60, a transition zone 82 and a monomerdeposition zone 66 as are identified in FIG. 1.

Once a polymeric material has been treated in accordance with theinvention, i.e., a surface of the polymeric material has a plasmadeposited coating thereon, the polymeric material may be subsequentlytreated prior to administration to a patient. For example, therapeuticagents may be applied to the polymeric surface having a plasma depositedcoating. Such therapeutic agents include anti-microbial agents,anti-fungal agents, anti-viral agents, anti-thrombogenic agents, and thelike. While not wishing to be bound by any particular theory, it isbelieved that plasma deposition of certain monomers (e.g.,N-vinyl-2-pyrrolidone) allows therapeutic agents to adsorb on thepolymeric surface. Preferably, applying therapeutic agents to polymericsurfaces having plasma deposited coatings thereon is accomplished insitu, i.e., at or near the point of administration to a patient becauseof sterility concerns.

Inside Diameter Surface Treatment

In an alternative embodiment of the present invention, an insidediameter surface of the tubing can be treated so as to improve itslubricity. To achieve ID treatment, an additional glow discharge zonecan be added to the apparatus shown in FIG. 1, wherein an ID treatmentzone is preferably located after the inert gas plasma pre-treatment zoneand prior to the monomer deposition zone.

Due to the permeability of silicone rubber, tubing 18 absorbs gas as itremains on reel 30 in bell 38, the gas equilibrating within the tubing18 ID usually at least an hour or so to fill the tubing 18 so that, asthe tubing 18 passes through capillary tube 14, it carries the dischargegas with it into the discharge zone between the electrodes, as shown inFIG. 6. If using tubing other than silicone, such other tubing not beingas readily permeable, a standing time of several additional hours allowsthe atmosphere of the chamber to permeate and/or to enter the tubingthrough its ends and equilibrate. Upon establishment of pulsed RF powersuch as that described with reference to FIG. 1, preferential dischargeoccurs within tubing 18 between the electrodes as the tubing passes fromreel 30 to bell 42 for collection. In this manner surface modificationof the slip characteristics of the ID of tubing 18 is effected, whethermerely by hardening or by coating, as desired and depending on the typeof gas used.

As shown in FIG. 6, inside the electrodes 20 and 22 is a section ofglass capillary 14 serving as a reactor, the capillary 14 having aninside diameter that is close fitting relative to the OD of thepolymeric tubing, i.e., the inner surface of the glass capillary 14 isclose enough to the OD surface of the polymeric tubing such that theglow discharge preferentially occurs on the ID surface of the tubing.For example, approximately 2 to 7% (about 5-7% being most preferred)greater than the outside diameter of the tubing 18 which is beingtreated is typically required in order for the glow to be preferentiallyproduced inside of the silicone tubing. When a space of greater thanabout 0.006 inch or about 7% exists between the tubing 18 and thecapillary 14, undesired discharge may occur in the space around theoutside of the tubing 18 and within the capillary 14 rather thanpreferentially inside of the tubing 18 only.

It can be seen from the foregoing description that the invention in itsmost preferred form presently comprises a plasma reactor and methodwhich produces a glow discharge within the lumen of small diametersilicone tubing for the purpose cross-linking and hardening the innersurface. This treatment can be performed continuously meaning thattubing is fed from a spool of 1000+ feet of tubing and treated as itmoves through an outer glow discharge zone and then an inner glowdischarge zone of the reactor then it passes into a receiving chamber.Various electrode configurations may be used but they all provide thebest performance when pulsed RF power is used in treating the ID surfaceof polymeric tubing. Magnetic fields can be used to enhance thedischarges and allow lower pressure operation and treatment ofmulti-lumen tubing.

Preferably, accomplishing a preferential glow discharge on the IDsurface of polymeric tubing is done by reactance coupling that utilizespower provided by a pulsed radio frequency power source. Morepreferably, the pulsed radio frequency power source provides acontinuous sequence of "on" periods and "off" periods, where the "on"periods having a duration of about 1 to about 10 milliseconds and the"off" periods have a duration of about 4 to about 800 milliseconds.

As described above, glow discharge treatments of both inside and outsideof the tubing described above may involve the use of "inert" gases. Gaspressure in the ID surface treatment zone is preferably maintained at arelatively higher pressure than the pre-treatment zone. This fills thetubing with inert gas to a stable pressure while the pre-treatment zoneis maintained at a relatively lower pressure which is more desirable forthe outer surface plasma treatment. These differential pressures aremaintained by using gas flow controls, orifices, and automatic exhaustvalve pressure controllers as will be known by those familiar with thisart.

In a variation on the above treatment, a polymerizable siloxane vapor,or other polymerizable gas e.g., silane or fluorocarbon may beintroduced into the ID surface treatment zone. The vapors permeate thetubing wall and, upon passing through the ID treatment zone, becomepolymerized as a coating inside of the tubing. This means that it isalso possible to deposit plasma polymers inside of silicone tubingwithout feeding the vapors through the end of the tube which would beimpractical in long, small diameter tubing.

The possible uses of this invention include any tubular device which hasa moving part in contact with the ID of silicone rubber tubing or anypolymer which exhibits a tacky surface, particularly those devices inwhich the contact occurs within the lumen of silicone tubing.

One advantage of treated tubing is the improved "stringability" itoffers for inserting wire torsion coils, guide wire, braided wire andthe like into the tubing through the lumen thereof. This is an importantadvantage in cases such as pacing leads for example where small wiresmust be threaded or pushed through the lumen over distances of two tofour feet, typically.

Heretofore, "stringability" has been accomplished by treating the tubingwith an agent such as FREON or hydrocarbons, such as heptane and thelike, to swell it and using isopropyl alcohol to wet the wire and lumenwhile pushing the wire into the lumen. All of this is now obviated bythe fact that tubing treated according to this invention will readilyaccept insertion of a wire or the like without any other treatment stepby merely pushing the wire into the lumen. This is due to the increasedand improved slip characteristics imparted to the tubing by thetreatment of this invention.

FIG. 7 is a simplified schematic view of an implantable medical device200 embodying the present invention, where at least one improved pacingand sensing lead 218 or 288 is attached to an hermetically sealedenclosure 214 and implanted near human heart 316. In the case whereimplanted medical device 200 is a pacemaker it includes at least one orboth of pacing and sensing leads 216 and 218. Pacing and sensing leads216 and 218 sense electrical signals attendant to the depolarization andre-polarization of the heart 316, and provide pacing pulses for causingdepolarization of cardiac tissue in the vicinity of the distal endsthereof. Implantable medical device 200 may be an implantable cardiacpacemaker such as those disclosed in U.S. Pat. No. 5,158,078 to Bennettet al, U.S. Pat. No. 5,312,453 to Shelton et al, or U.S. Pat. No.5,144,949 to Olson, all hereby incorporated herein by reference in theirrespective entireties.

Implantable medical device 200 may also be a PCD(Pacemaker-Cardioverter-Defibrillator) corresponding to any of thevarious commercially available implantable PCDs, with the substitutionof pacing or sensing leads connector module 212 of the present inventionfor the connector block assembly otherwise present. The presentinvention may be practiced in conjunction with PCDs such as thosedisclosed in U.S. Pat. No. 5,545,186 to Olson et al., U.S. Pat. No.5,354,316 to Keimel, U.S. Pat. No. 5,314,430 to Bardy, U.S. Pat. No.5,131,388 to Pless or U.S. Pat. No. 4,821,723 to Baker et al., allhereby incorporated herein by reference in their respective entireties.Those devices may be employed directly in conjunction with the presentinvention, and most preferably are practiced such that the feedthroughsinterconnecting the circuitry therein to their connector blocks islocated to permit ready access between the feedthroughs and theelectrical connectors disposed within the connector bores of connectoror header module 212.

Alternatively, implantable medical device 200 may be an implantablenerve stimulator or muscle stimulator such as that disclosed in U.S.Pat. No. 5,199,428 to Obel et al., U.S. Pat. No. 5,207,218 to Carpentieret al. or U.S. Pat. No. 5,330,507 to Schwartz, or an implantablemonitoring device such as that disclosed in U.S. Pat. No. 5,331,966issued to Bennet et al., all of which are hereby incorporated byreference herein in their respective entireties. The present inventionis believed to find wide application to any form of implantableelectrical device for use in conjunction with electrical leads, and isbelieved to be particularly advantageous in those contexts wheremultiple medical electrical leads are employed and desired.

In general, hermetically sealed enclosure 214 includes anelectrochemical cell such as a lithium battery, circuitry that controlsdevice operations and records arrhythmic EGM episodes, and a telemetrytransceiver antenna and circuit that receives downlink telemetrycommands from and transmits stored data in a telemetry uplink to theexternal programmer. The circuitry and memory may be implemented indiscrete logic or a micro-computer based system with A/D conversion ofsampled EGM amplitude values. The particular electronic features andoperations of the implantable medical device are not believed to be ofoverriding significance in respect of practicing the present invention.One exemplary operating system is described in commonly assigned,co-pending U.S. patent application Ser. No. 08/678,219, filed Jul. 11,1996, for "Minimally Invasive Implantable Device for MonitoringPhysiologic Events," the disclosure of which is hereby incorporated byreference herein in its entirety.

It is to be understood that the present invention is not limited inscope to either single-sensor or dual-sensor pacemakers, and that othersensors besides activity and pressure sensors could be used inpracticing the present invention. Nor is the present invention limitedin scope to single-chamber pacemakers. The present invention may also bepracticed in connection with multiple-chamber (e.g., dual-chamber)pacemakers.

FIG. 8 depicts connector module 212 and hermetically sealed enclosure214 of implantable medical device or dual chamber pacemaker IPG 200 asthey relate to a patient's heart 316. Atrial and ventricular pacingleads 216 and 218 extend from connector header module 212 to the rightatrium and ventricle, repsectively. Atrial electrodes 220 and 221disposed at the distal end of the atrial pacing lead 216 are located inthe right atrium. Ventricular electrodes 228 and 229 at the distal endof ventricular pacing lead 218 are located in the right ventricle.

FIG. 9 shows a block diagram illustrating the constituent components ofa pacemaker 310 in accordance with one embodiment of the presentinvention, where pacemaker 310 has a microprocessor-based architecture.The present invention may be utilized in conjunction with otherimplantable medical devices, however, such as cardioverters,defibrillators, cardiac assist systems, and the like, or in conjunctionwith other design architectures.

In the illustrative embodiment shown in FIG. 9, pacemaker 310 includesan activity sensor 312, which is preferably a piezoceramic accelerometerbonded to the hybrid circuit inside the pacemaker housing. Piezoceramicaccelerometer sensor 312 provides a sensor output which varies as afunction of a measured parameter that relates to the metabolicrequirements of patient.

Pacemaker 310 of FIG. 9 is most preferably programmable by means of anexternal programming unit (not shown in the Figures). One suchprogrammer suitable for the purposes of the present invention is thecommercially available Medtronic Model 9790 programmer. The programmeris a microprocessor device which provides a series of encoded signals topacemaker 310 by means of a programming head which transmitsradio-frequency (RF) encoded signals to pacemaker 310 according to atelemetry system such as that described in U.S. Pat. No. 5,312,453 toWyborny et al., the disclosure of which is hereby incorporated byreference herein in its entirety. It is to be understood, however, thatthe programming methodology disclosed in Wyborny et al. patent isidentified herein for the illustrative purposes only, and that anyprogramming methodology may be employed so long as the desiredinformation is transmitted to and from the pacemaker. One of skill inthe art may choose from any of a number of available programmingtechniques to accomplish this task.

Pacemaker 310 is schematically shown in FIG. 9 to be electricallycoupled to a pacing lead 318 disposed in patient's heart 316. Lead 318preferably includes an intracardiac electrode disposed at or near itsdistal end and positioned within the right ventricular (RV) or rightatrial (RA) chamber of heart 316. Lead 318 may have unipolar or bipolarelectrodes disposed thereon, as is well known in the art. Although anapplication of the present invention in the context of a single-chamberpacemaker is disclosed herein for illustrative purposes, it is to beunderstood that the present invention may equally well be applied in thecontext of a dual-chamber pacemakers or other implantable device.

Lead 318 is coupled to a node 250 in the circuitry of pacemaker 310through input capacitor 252. In the presently disclosed embodiment,accelerometer 312 is attached to the hybrid circuit inside pacemaker310, and is not shown explicitly in FIG. 9. The output fromaccelerometer 312 is coupled to input/output circuit 254. Input/outputcircuit 254 contains analog circuits for interfacing to heart 316,accelerometer 312, antenna 256, and circuits for the application ofstimulating pulses to heart 316 to control its rate under control ofsoftware-implemented algorithms in microcomputer circuit 258.

Microcomputer circuit 258 preferably comprises on-board circuit 260 andoff-board circuit 262. Circuit 258 may correspond to the microcomputercircuit disclosed in U.S. Pat. No. 5,312,453 to Shelton et al. thedisclosure of which is hereby incorporated by reference herein in itsentirety. On-board circuit 260 includes microprocessor 264, system clockcircuit 266, and on-board RAM 268 and ROM 270. In the presentlydisclosed embodiment of the invention, off-board circuit 262 comprises aRAM/ROM unit. On-board circuit 260 and off-board circuit 262 are eachcoupled by a data communication bus 272 to a digital controller/timercircuit 274. Microcomputer circuit 258 may form a custom integratedcircuit device augmented by standard RAM/ROM components.

The electrical components shown in FIG. 9 are powered by an appropriateimplantable battery power source 276, in accordance with common practicein the art. For the sake of clarity, the coupling of battery power tothe various components of pacemaker 310 is not shown in the Figures.

Antenna 256 is connected to input/output circuit 254 to permituplink/downlink telemetry through RF transmitter and receiver unit 278.Unit 278 may correspond to the telemetry and program logic disclosed inU.S. Pat. No. 4,566,063 issued to Thompson et al., hereby incorporatedby reference herein in its entirety, or to that disclosed in theabove-referenced Wyborny et al. patent. The particular programming andtelemetry scheme chosen is not believed to be critical for purposes ofpracticing the present invention so long as entry and storage of valuesof rate-response parameters are permitted.

V_(REF) and Bias circuit 282 generates a stable voltage reference andbias currents for the analog circuits of input/output circuit 254.Analog-to-digital converter (ADC) and multiplexer unit 284 digitizesanalog signals and voltages to provide "real-time" telemetryintracardiac signals and battery end-of-life (EOL) replacement function.

Operating commands for controlling the timing of pacemaker 310 arecoupled by data bus 272 to digital controller/timer circuit 274, wheredigital timers and counters establish the overall escape interval of thepacemaker as well as various refractory, blanking and other timingwindows for controlling the operation of the peripheral componentsdisposed within input/output circuit 254.

Digital controller/timer circuit 274 is preferably coupled to sensingcircuitry, including sense amplifier 288, peak sense and thresholdmeasurement unit 290 and comparator/threshold detector 292. Circuit 274is further preferably coupled to electrogram (EGM) amplifier 294 forreceiving amplified and processed signals sensed by an electrodedisposed on lead 318. Sense amplifier 288 amplifies sensed electricalcardiac signals and provides an amplified signal to peak sense andthreshold measurement circuitry 290, which in turn provides anindication of peak sensed voltages and measured sense amplifierthreshold voltages on multiple conductor signal path 367 to digitalcontroller/timer circuit 274. An amplified sense amplifier signal isthen provided to comparator/threshold detector 292. Sense amplifier 288may correspond to that disclosed in U.S. Pat. No. 4,379,459 to Stein,which is hereby incorporated by reference herein in its entirety.

The electrogram signal provided by EGM amplifier 294 is employed whenthe implanted device is being interrogated by an external programmer(not shown) to transmit by uplink telemetric means a representation ofan analog electrogram of the patient's electrical heart activity. See,for example, U.S. Pat. No. 4,556,063 to Thompson et al., herebyincorporated by reference herein in its entirety. Output pulse generator296 provides pacing stimuli to patient's heart 316 through couplingcapacitor 298 in response to a pacing trigger signal provided by digitalcontroller/timer circuit 274 each time the escape interval times out, anexternally transmitted pacing command is received, or in response toother stored commands as is well known in the pacing art. Outputamplifier 296 may correspond generally to the output amplifier disclosedin U.S. Pat. No. 4,476,868 to Thompson, also incorporated by referenceherein in its entirety.

While specific embodiments of input amplifier 288, output amplifier 296and EGM amplifier 294 have been identified herein, this is done for thepurposes of illustration only. The specific embodiments of such circuitsare not critical to practicing the present invention so long as thecircuits provide means for generating a stimulating pulse and arecapable of providing digital controller/timer circuit 274 with signalsindicative of natural or stimulated contractions of the heart.

EXAMPLES

While polymeric surface treatment methods and apparatuses in accordancewith the invention have been described herein, the followingnon-limiting examples will further illustrate the invention.

Conventional silicone tubing (0.5 inch outer diameter, available fromCole-Parmer Inc., Vernon Hills, Ill.) was loaded in an upper chamber,shown as 38, of an apparatus as shown in FIG. 1, described above. Theupper chamber was evacuated. Argon gas flow was started at 1 sccm intothe upper chamber. The parameters set for a throttle valve for the upperchamber and a constant RF (radio frequency) power in the plasmapre-treatment zone are shown in Table 2, below. An argon discharge beganin the plasma pre-treatment zone.

The monomer used was N,vinyl-2-pyrrolidone (NVP) (99.5% optical grade,redistilled, available from Polysciences, Inc., Warrington, Pa.) and wasplaced in the monomer reservoir, shown as 52 in FIG. 4. The temperaturesof the monomer source (including the reservoir and the conduit), RFpower level, pulse width used are indicated in Table 2, below.

                  TABLE 2                                                         ______________________________________                                        Condition  Example 1                                                                              Example 2 Example 3                                                                            Example 4                                ______________________________________                                        Throttle valve                                                                           400 mT   400 mT    400 mT 400 mT                                   setting (pre-treat.                                                           zone)                                                                         Power level (Pre-                                                                        20 watts 40 watts  40 watts                                                                             40 watts                                 treat. zone)                                                                  Monomer temp.                                                                            51° C.                                                                          51° C.                                                                           51° C.                                                                        51° C.                            (reservoir/                                                                   conduit)                                                                      Throttle valve                                                                           500 mT   500 mT    500 mT 500 mT                                   setting (monomer                                                              deposition zone)                                                              Power level                                                                              8 watts/ 8 watts/  4 watts/                                                                             8 watts/                                 (monomer    0 watts  0 watts   0 watts                                                                              0 watts                                 deposition zone)                                                              Power Pulse                                                                              4 milli- 4 milli-  4 milli-                                                                             4 milli-                                 width (monomer                                                                                seconds                                                                           seconds   seconds                                                                              seconds                                  deposition zone)                                                              Duty Cycle 20%      20%       20%    20%                                      Line Speed 3.2 inches/                                                                            3.2 inches/                                                                             3.2 inches/                                                                          8.8 inches/                                         min.     min.      min.   min.                                     ______________________________________                                    

A bluish colored glow discharge was observed in the deposition zone whenthe NVP flow started. The monomer deposition zone was run in this mannerfor 20 minutes so that about 5 feet of tubing had monomer deposited onthe outer surface.

Tubing from Examples 1-4 were then soaked for 24 hours in deionizedwater and then evaluated for % retention of the monomer based on FTIRanalysis. Each of the treated tubing examples was analyzed usingfourrier transform infra-red (FTIR) spectroscopy to detect plasmadeposited NVP coatings on the polymeric surface. A BIORAD FTS-175spectrometer equipped with a UMA500 infrared microscope was used toobtain micro-attenuated total reflectance (ATR) spectra of the examplesimmediately following plasma deposition and after the same tubingsegments of the examples were soaked in deionized water for 24 hours atroom temperature, and then dried. Infrared absorbance peak intensitiesfor 1680 cm⁻¹ (carbonyl absorbance from NVP) and 1015 cm⁻¹ (Si--O--absorbance from silicone tubing) were recorded as shown in Table 3.

FIG. 10 is an overlay FTIR spectrum of silicone tubing treated inaccordance with the invention from Example 2 after soaking in deionizedwater for 24 hours (reference numeral 706). Comparative samples werealso analyzed and appear on the overlay: NVP monomer alone (referencenumeral 702), PVP polymer alone (reference numeral 704) and untreatedsilicone tubing (reference numeral 708).

The data in Table 3 shows the FTIR results from Examples 1-4, bothbefore and after soaking 24 hours in deionized water.

                  TABLE 3                                                         ______________________________________                                                                          1680 cm.sup.-1 /                            Example     1680 cm.sup.-1                                                                           1015 cm.sup.-1                                                                           1015 cm.sup.-1                              ______________________________________                                        1 - pre-soak                                                                              0.04149    0.09752    0.4255                                      1 - post-soak                                                                             0.002      0.45068    0.0044                                      2 - pre-soak                                                                              0.02064    0.0488     0.4230                                      2 - post-soak                                                                             0.00556    0.13019    0.0427                                      3 - pre-soak                                                                              0.02019    0.07735    0.2610                                      3 - post-soak                                                                             0.0025     0.19178    0.0130                                      4 - pre-soak                                                                              0.02359    0.1862     0.1267                                      4 - post-soak                                                                             0.002      0.24798    0.0081                                      ______________________________________                                    

The results shown in FIG. 10 were calculated based on the relativeinfrared absorbance peak values at 1680 cm⁻¹ divided by the peak valuesat 1015 cm⁻¹ which indicates the relative quantity of ppNVP (plasmapolymerized NVP) on the surface of each tubing before and after soaking,as shown by the data in Table 3. Example 2 retained over 25% of its FTIRintensity after soaking and rinsing in deionized water (see, FIG. 10 forspectrum). Examples 1, 3 and 4 were in the 5-12% range (see, FIG. 11 forretention percentages after soaking).

It is believed that the pre-soak absorbance values for the 1680 cm⁻¹ NVPabsorbance were artificially high due to the presence of residualmonomer vapors within the ppNVP-silicone tubing matrix immediatelyfollowing plasma deposition. Soaking of the tubing in deionized waterfor 24 hours was done to remove this residual monomer and any of theplasma deposited coating that may have been soluble and not attached tothe silicone surface.

The tubing from Examples 1-4 were then evaluated in a Friction Testusing a modified "Coefficient of Friction of Plastic Film and Sheeting"(Sled Test, ASTM 1894-78). A slip/peel tester (Instrumentors SP-102BSlip/Peel Tester) provided a moving platen with speed control and loadcell. A custom bed, which was attached to the platen, held the samplesof tubing. A sled with a polished stainless steel bottom was draggedover the samples of the tubing. The test set-up was as follows: variablebed speed of 5 inches/minute; data collection using a data acquisitionboard; and load cells. The test procedure involved setting the bed speedto 6 inches/min.; the outer surface of the tubing samples were wipedwith water and mounted to the bed; the sled was wiped with acetone andplaced on the samples and the force data acquired with the dataacquisition board. The data collected represented the force orhorizontal load required to displace the weighted sled. Twomodifications were made to this test to allow for "wet" testing. First,the tubing bed was placed in a shallow pan which was filled withdeionized water for testing. Steel rods were inserted inside of thetubing samples to prevent them from floating in the filled pan.

FIG. 12 is a graphic representation of repeated friction tests performedin an aqueous environment with tubing treated in accordance with theinvention. Comparative examples of untreated silicone tubing (referencenumeral 902) and a commercially available surface modified tubing(BIOCOAT on polyurethane, available from Biocoat Incorporated, FortWashington, Pa.) were also run with a sample of silicone tubing treatedas in Example 3 above (reference numeral 904). The friction testperformed in a shallow pan of water, as described above, was repeatedwith the same tubing samples 20 times. As can be seen, both the plasmaNVP coated Example 3 and the BIOCOAT sample provide much lower frictionthan untreated silicone tubing immediately following immersion in water.However, the plasma NVP sample maintained its low friction surfacethrough the course of 20 repeated pull tests, while the BIOCOAT samplegradually increased in friction over the 20 pulls. This suggests thatthe plasma NVP surface is likely more stable and relatively betteradhered than the comparative BIOCOAT surface.

FIG. 13 is a graphic representation of friction tests performed in anaqueous environment with tubing treated in accordance with theinvention, as in Examples 1-4 above. Comparative examples were alsoevaluated. Comparative example A was untreated silicone tubing,Comparative example B was inert gas plasma treated tubing, andComparative example C was plasma deposited siloxane on silicone tubing.The data indicates that inert gas plasma reduces friction byapproximately one third while the siloxane and plasma NVP depositionsreduce friction to less than about half, as compared to untreatedsilicone.

The above disclosure is intended to be illustrative and not exhaustive.The description will suggest many variations and alternatives to one ofordinary skill in this art. All these alternatives and variations areintended to be included within the scope of the attached claims. Thosefamiliar with the art may recognize other equivalents to the specificembodiments described herein which equivalents are also intended to beencompassed by the claims attached thereto.

What is claimed is:
 1. A polymeric tubing comprising:a tubing wallhaving an outer diameter surface and an inner diameter surface formingat least one lumen therein, wherein the outer diameter surface comprisesa surface treated by exposure to a plasma glow discharge in the presenceof an inert gas and deposition of a monomer for a time sufficient tomodify the slip characteristics of the outer diameter surface.
 2. Thetubing of claim 1 wherein exposure to a plasma glow discharge comprisesexposing the outer diameter surface to the plasma glow discharge for atime sufficient to reduce the coefficient of sliding friction of thetreated outer diameter surface by at least 70%.
 3. The tubing of claim 1wherein exposure to a plasma glow discharge comprises exposing the outerdiameter surface to the plasma glow discharge for a time sufficient toreduce the coefficient of sliding friction of the treated outer diametersurface as measured after a 24 hour exposure to an aqueous environment.4. The polymeric tubing of claim 1 wherein exposure to a plasma glowdischarge comprises exposing a silicone tubing wall to the plasma glowdischarge.
 5. The polymeric tubing of claim 1 wherein deposition of themonomer comprises deposition of N-vinyl-2-pyrrolidone.
 6. The polymerictubing of claim 1 wherein the outer diameter surface comprises a surfaceto which a therapeutic agent is applied, after exposure to a plasma glowdischarge.